Communication devices and methods

Abstract

A first communication device is configured to communicate with a third communication device in coordination with a second communication device. The first communication device comprising circuitry configured to: transmit a sounding information to the third communication device, receive channel feedback information from the third communication device in response to the sounding information, determine alignment configuration information based on the channel feedback information and transmit the alignment configuration information to the second communication device, or receive the alignment configuration information from the third communication device and determined by the third communication device based on the sounding information, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the second communication device.

Description

COMMUNICATION DEVICES AND METHODSBACKGROUNDFIELD OF THE DISCLOSURE

[0001] The present disclosure relates to communication devices and methods, in particular for coordinated communication.DESCRIPTION OF RELATED ART

[0002] High reliability and range extension are required for wireless Internet of Things (loT) applications to provide robust wireless communication with a small number of access points tominimize capital investment. Range extension is essentially improving the signal-to-noise ratio (SNR). Relay networks and / or Joint Transmission (JT) are considered as techniques to achieve this goal. Wi-Fi Alliance has standardized EasyMesh to establish relay networks on WLAN even in home usage scenario. In addition, 3GPP (Third Group Partnership Project) has defined JT, which improves SNR for users at the edge of overlapping cells.

[0003] Relay networks improve the SNR of users far away from source nodes, but many relay nodes are required to cover an entire service area. Joint transmission allows transmitters (e.g. access points) to act as one transmitter with more transmit power and antennas, which can be used to expand the cell size of transmitters, especially under transmit power regulation.

[0004] As mentioned above, JT has been standardized and adopted in the 3GPP standards. JT can generally be referred to as coordinated communication, in which two or more communication devices transmit at least part of the same data to a third communication device. JT comes in two types: Coherent Joint Transmission (CJT) and Non-Coherent Joint Transmission (NCJT). The main difference between the two types is how transmitters wishing to use JT can derive beamforming steering matrices and achieve the required synchronization accuracy.

[0005] CJT allows two or more access points (APs) to act as a virtual AP for station (STA). To do this, overall channel state information must be known in order to derive a common steering matrix for the participating APs. This means that channel state information (CSI) for each channel between the participating APs and the STA to be served must be determined and made available to at least one of the participating APs in order to compute a common steering matrix. NCJT, on the other hand, requires less synchronization between the participating APs. For NCJT, it is sufficient for each AP to know its own CSI with respect to the STA to be served. CJT generally achieves better performance because SNR and spatial stream improvement can be achieved simultaneously. NCJT, on the other hand, requires less synchronization and therefore has less overhead.

[0006] NJCT comes in two flavors: Diversity mode and Multiplexing mode. In diversity mode, APs send the same data to the STA to improve SNR or diversity gain. In multiplexing mode, the number of spatial streams with different data is increased to improve throughput to the STA.

[0007] As described above, diversity mode NCJT provides SNR improvement while requiring less synchronization between APs. However, the loose coordination can result in signal cancellation because the steering matrices are computed at each AP individually. Accordingly, there is no guarantee that a signal received from a first AP and a signal received from a second AP will be in phase when received by an STA. However, if the received signals are out of phase, a combined received signal at the STA may be less than each individually received signal or may be completely canceled.

[0008] Moreover, signal cancelation may also happen due to timing detection differences. The reason for this is that timing detection doesn’t always provide the same result and may thus cause unintentional phase shift of received signals. It may happen that one AP starts to send a signal a little earlier than another AP due to clock differences, which can cause a phase shift of the received signals. The amount of the phase shift depends on the used subcarrier frequency in baseband and the actual time difference between correct timing and detected timing if a frequency clock of each device is the same.

[0009] Phase-shift is a well-known phenomenon that is also exploited actively in other situations, such as for diversity gain in Multi-Input Multi-Output (MIMO) technologies. By correlating multiple received signals with different phases, signal reception can be improved due to the diversity in phase.

[0010] Another related technology is weight synchronization for CJT, which is described in detail in US 2023 / 0141791 A1. As mentioned above, CJT requires transmitters to derive a common steering matrix from an overall CSI. If the overall CSI is fed back to the transmitters from a beamformee, each transmitter can derive the common steering matrix and the steering matrix does not need to be shared afterwards. However, most algorithms for deriving the common steering matrix rely on Eigen Vector Decomposition (EVD) or Singular Vector Decomposition (SVD), and the eigenvectors derived at different APs aren't necessarily the same due to the way these algorithms work. The reason for this is that the first eigenvector of a matrix X can be expressed as, where <p is an arbitrary real number. Accordingly, steering matrices derived by different APs aren’t synchronized due to their different EVD / SVD algorithms. Thiscan be solved according to US 2023 / 0141791 A1 by sending an indication of < > to the individual APs.

[0011] The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventor(s), to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.SUMMARY

[0012] It is an object to facilitate use of joint transmission, in particular avoid signal cancellation when using NCJT in diversity mode.

[0013] According to an aspect there is provided a first communication device configured to communicate with a third communication device in coordination with a second communication device, the first communication device comprising circuitry configured to: transmit a sounding information to the third communication device, receive channel feedback information from the third communication device in response to the sounding information, determine alignment configuration information based on the channel feedback information and transmit the alignment configuration information to the second communication device, or receive alignment configuration information from the third communication device, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the second communication device.

[0014] According to a further aspect there is provided a second communication device configured to communicate with a third communication device in coordination with a first communication device, the second communication device comprising circuitry configured to: receive a sounding information for the third communication device,receive channel feedback information from the third communication device in response to the sounding information, receive, from the first communication device or the third communication device, alignment configuration information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the first communication device based on the received alignment configuration information.

[0015] According to a further aspect there is provided a third communication device configured to receive data in a coordinated communication from a first communication device in coordination with a second communication device, the third communication device comprising circuitry configured to: receive a sounding information from at least one of the first communication device and the second communication device, determine alignment configuration information based on the sounding information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, transmit, in response to a request by at least one of the first communication device and the second communication device, the alignment configuration information to the first communication device and the second communication device, and receive from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.

[0016] According to still further aspects corresponding methods, a computer program comprising program means for causing a computer to carry out the steps of the method disclosed herein, when said computer program is carried out on a computer, as well as a non -transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method disclosed herein to be performed are provided.

[0017] Embodiments are defined in the dependent claims. It shall be understood that the disclosed methods, the disclosed computer program and the disclosed computer-readable recording medium have similar and / or identical further embodiments as the claimed access points and stations and as defined in the dependent claims and / or disclosed herein.

[0018] One aspect of the disclosure is to determine alignment configuration information based on sounding information or channel feedback information. The alignment configuration information includes subcarrier selection information and / or phase alignment information. The information may be used for alignment operations by communication devices (e.g., APs) that transmit at least partially the same data to another communication device (e.g., STA) in a coordinated communication. In other words: The first communication device and the second communication device can communicate with the third communication device in a coordinated communication based on the alignment configuration information Thereby, JT operations can be further enhanced by mitigating phase misalignment.

[0019] The foregoing paragraphs have been provided by way of general introduction and are not intended to limit the scope of the following claims. The described embodiments, together with further advantages, will be best understood by reference to the following detailed description taken in conjunction with the accompanying drawings.BRIEF DESCRIPTION OF THE DRAWING

[0020] A more complete appreciation of the disclosure and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein:Fig. 1 shows a schematic diagram illustrating a typical constellation of three communication device communicating with each other.Fig. 2A shows a schematic diagram illustrating an example of NCJT.Fig. 2B shows a schematic diagram illustrating an example of CJT.Fig. 3A shows a frame exchange sequence illustrating a sounding procedure.Fig. 3B shows a frame exchange sequence illustrating a coordinated sounding procedure.Fig. 4 shows a schematic diagram illustrating timing detection for WLAN.Fig. 5 shows a frame exchange sequence illustrating timing detection differences.Fig. 6 shows a schematic diagram illustrating an example of an embodiment of the present disclosure.Fig. 7 shows a frame exchange sequence illustrating an example of an embodiment of the present disclosure.Fig. 8 shows a frame diagram illustrating a first example of a phase alignment frame.Fig. 9 shows a frame diagram illustrating a second example of a phase alignment frame.Fig. 10 shows a schematic diagram illustrating subcarrier mapping according to an embodiment of the present disclosure.Fig. 11 shows as frame diagram illustrating an example of signaling for NCJT within a PPDll according to an embodiment of the present disclosure.Fig. 12 shows a frame exchange sequence illustrating an example of a further embodiment of the present disclosure.Fig. 13 shows a frame diagram illustrating additional fields included in a feedback frame according to an embodiment of the present disclosure.Fig. 14 shows a flow chart of an embodiment of a first communication method of a first communication device.Fig. 15 shows a flow chart of an embodiment of a second communication method of a second communication device.Fig. 16 shows a flow chart of an embodiment of a third communication method of a third communication device.DETAILED DESCRIPTION OF THE EMBODIMENTS

[0021] Referring now to the drawings, wherein like reference numerals designate identical or corresponding parts throughout the several views, Fig. 1 shows a schematic diagram illustrating a typical constellation of three communication device that communicate with each other. Specifically, Fig. 1 shows a first access point device (AP1), a second access point device (AP2) and a station device (STA). The STA is in range of both APs and both APs can communicate with the STA to exchange data. In the following, the first access point device may be referred to as “a first communication device”, the second access point may be referred to as “a second communication device”, and the station device may be referred to as “a third communication device”.

[0022] Typically, beamforming technology is used for the communication shown in Fig. 1. Beamforming is a technique used to improve the SNR of received signals, eliminate unwanted sources of interference, and focus transmitted signals at specific locations. Beamforming is central to sensor array systems, including MIMO wireless communication systems such as 5G, LTE, and WLAN. In Fig. 1 , a first beam 101 from the first AP to the STA and a second beam 102 from the second AP to the STA are shown as examples.

[0023] In the following description, the term "beamformer" refers to a communication device that transmits a physical layer (PHY) protocol data unit (PPDU) using a beamforming steering matrix w.The term "beamformee" refers to a communication device that receives a PPDU transmitted using a beamforming steering matrix w. The terms "(channel) sounding" refers toa technique that evaluates a wireless channel. Typically, a beamformer sends a beamformee known sequences, which allows to the beamformee to calculate channel state information (CSI), and the CSI is fed back to the beamformer. Finally, the terms "steering matrix" refers to a matrix determined using knowledge of the channel between a transmitter and an intended receiver that maps from space-time streams to transmit antennas with the goal of improving the signal power or the SNR at the intended receiver and / or mitigating interference signal power at the unintended receiver. In the example according Fig. 1 , both APs are beamformers and the STA is a beamformee.

[0024] For a situation as shown in Fig. 1 , JT technology has been envisioned. JT is the concurrent data transmission from multiple coordinated APs to a STA. Therefore, in the following, JT is also generally referred to as coordinated communication.

[0025] In JT, the first AP and the second AP may at least partially transmit the same data to the STA. The benefits of JT are an improved Signal-to-lnterference-Plus-Noise Ratio (SINR) for cell-edge users and an improved system throughput.

[0026] Fig. 2A and Fig. 2B illustrate two types of JT. Fig. 2A illustrates Non-Coherent Joint Transmission (NCJT), and Fig. 2B illustrates Coherent Joint Transmission (CJT).

[0027] In Fig. 2B, AP1 and AP2 operate as a single virtual AP to serve the STA. For this to work, AP1 and AP2 have to negotiate with each other to calculate a common steering matrix (WCJT ). The common steering matrix will subsequently be used by both APs to prepare beams for transmission to the STA. Beams from each AP are formed using the common steering matrix as indicated here by the single beam 201. In this approach, AP1 and AP2 require precise synchronization. CJT communicating can be expressed by the following formular:where S-L is a data symbol to be transmitted from AP1 and AP2. wC]Tis the common steering matrix derived at AP1 and / or AP2. h and h2are CSI of the channel from AP1 to STA and CSI of the channel from AP2 to STA, respectively. PCJTis a postcoding matrix for CJT.

[0028] In Fig. 2A, NCJT is applied. Thus, AP1 and AP2 also cooperate with each other to serve the STA. However, in this approach less synchronization between AP1 and AP2 is required. As outlined before, NCJT comes in two flavors: Diversity mode and Multiplexing mode.

[0029] Diversity mode can be expressed as follows:where s0is a data symbol to be transmitted from AP1 and AP2. w1and w2are steering matrices derived at AP1 and AP2 forand h2are CSI of the channel from AP1 to STA and CSI of the channel from AP2 to STA, respectively. PDis a postcoding matrix for NCJT in Diversity mode.

[0030] Multiplexing mode can be expressed as follows:where S-L and s2are data symbol to be transmitted from AP1 and AP2, respectively. w1and iv2are steering matrices derived at AP1 and AP2 for NCJT, respectively.and h2are CSI of the channel from AP1 to STA and CSI of the channel from AP2 to STA, respectively. PMis a postcoding matrix for NCJT in Multiplexing mode.

[0031] Regarding postcoding for NCJT in diversity mode, Maximum Ratio Combination (MRC) is the preferred approach to further improve SNR. It can be expressed as:PM= K h1w1+ h2W2Hwhere K is a normalization factor and xHis a Hermitian transpose of vector x.

[0032] Fig. 3A and 3B illustrate channel sounding for JT. CSI acquisition is necessary to perform optimal beamforming at transmitters. Generally, it is recommended that channel sounding should be jointly performed when acquiring CSI for CJT. However, for NCJT this is notrequired, since w, (j = 1,2) is not derived from hj (j = 1,2, j #= j) but only from ht. o derive wC]T(i.e. the common steering matrix for CJT), on the other hand, all CSI has to be available.

[0033] Fig. 3A is a schematic diagram illustrating an example for a channel sounding scheme (e.g. for NCJT), and Fig. 3B is a schematic diagram illustrating an example for a coordinated channel sounding scheme (e.g. for CJT or NCJT). The latter is also referred to as joint sounding.

[0034] In Fig. 3A, each AP performs channel sounding separately. In Fig. 3B, channel sounding is performed simultaneously and in coordination. In both cases, a Null Data Packet Announcement (NDPA) 301 A, 301 B is sent before Null Data Packets (NDPs) 302A, 302B are sent, wherein an NDPA is a known sequence to be used for channel estimation at an STA to inform the parameters of the NDPs. After receiving the NDPs, channel estimation is performed, and the STA transmits CSI feedback (CSI-FBCK) 303 to the APs (i.e., AP1 and AP2). A CSI-FBCK format in the case of Fig. 3A is defined in IEEE 802.11. The same format would also be applicable for Joint Sounding as shown in Fig. 3B. Two formats of CSI-FBCK are generally known: Non-compressed FBCK and compressed FBCK. Both formats essentially transmit eigenvectors of the estimated channel matrix. In Non-Compressed FBCK, the bottom element of each eigenvector is set to an arbitrary complex number, while in Compressed FBCK it is set to one.

[0035] In Joint Sounding (Fig. 3B), a sounding trigger 304 is sent from one AP (e.g. AP1) to another AP (e.g. AP2) to initiate the sounding procedure. The sounding trigger 304 is sent before the one AP sends its NDPA 301 A so that all APs can send their NDPAs 301 B and NDPs 302B essentially at the same time with the one AP. It is assumed that the other APs (e.g. AP2) transmit their NDP 302B a certain time (e.g. 16usec) after the sounding trigger 304 has been received from the one AP. The one AP, on the other hand, sends its NDP 302A a certain time after the sounding trigger 304 has been sent.

[0036] If, in the example of Fig. 3B, AP1 and AP2 can establish a wired connection to another device (hereinafter referred to as the Master AP) that can control both AP1 and AP2 simultaneously,a sounding trigger 304 can also be sent from the Master AP. In the example of Fig. 3B, AP1 can be the Master AP.

[0037] With reference to Fig. 4, timing detection for WLAN is described below. In IEEE 802.11, a long training field (LTF) consisting of a known sequence can be prepended to a data portion of a transmission packet. The known sequence of the LTF can be used to estimate a channel for decoding. Since WLAN uses random channel access, the known sequence also works for timing detection to identify which samples are the first samples of which fields. Fig. 4 is a schematic diagram illustrating an exemplary LTF structure 400, where guard intervals (Gl) 401 are prepended to known sequences 402 (or LTF subblocks), and a set of Gl and the known sequence are repeated several times, each set prepended to the previous set.

[0038] As a timing detection algorithm, a cross correlation function is typically adopted when leveraging LTF. IEEE 802.11 also adopts an Orthogonal Frequency Domain Multiplexing (OFDM) waveform and consecutive NFFTsymbols from the detected symbol are converted in frequency domain by FFT (Fast Fourier Transform), where NFFTis the number of FFT points. Fig. 4 illustrates that a known sequence is put into a FFT window if a symbol at the white star 403 is detected as the first symbol of the known sequence.

[0039] However, such timing detection doesn’t always work to grasp the first symbol of the known sequence. For example, in Fig. 4, the sample located at the white star 403 should be detected as the first sample of a LTF subblock, but the former symbol (depicted at black star 404) could be detected as the first symbol improperly, and thus different consecutive symbols are put into the FFT window. Fortunately, the Gl is a cyclic prefix (CP) of the LTF subblock and the improper consecutive symbols still can be decoded by FFT, if all delay waves are observed at the symbol depicted at the black star 404. Although the improper timing detection affects demodulated signal with phase shift, receivers can demodulate a received signal correctly, because the following FFT windows also pick up symbols based on the improperly detected symbol.

[0040] In view of the above presented general background, the phenomenon of signal cancelation in diversity-mode NCJT will be explain in more detail below. As mentioned before, diversity-mode NCJT yields SNR improvement while requiring less synchronization accuracy among transmitters. However, diversity-mode NCJT can suffer from signal cancelation because each steering matrix is calculated at each AP individually. Assuming that each of two APs has n transmit antennas, and a STA has one receive antenna, a received signal y can be expressed as follows:where htis the channel from AP #i to STA,is the steering matrix of AP #i, and s is the data symbol to be transmitted.

[0041] However, it cannot be ensured that+ h2w21 is enough magnitude for demodulation, and signal cancelation can be observed if+ h2w21 is much less. As will be described below, at least one AP has to know h1w1+ h2w2and a should modify its steering matrix to avoid signal cancelation.

[0042] However, even if the AP knows h1w1+ fi2iV2, signal cancelation may still happen due to timing detection differences (as explained above with reference to Fig. 4). For example, as illustrated in Fig. 5, AP1 and AP2 each perform channel sounding to the STA separately (cf. Fig. 3A). After the channel sounding is completed, a trigger frame indicating start of NCJT is transmitted, and the APs perform NCJT. In the following, it is assumed that AP1 and AP2 have a completely estimated CSI (i.e. , h±and h2respectively) and both channels are static over time. If the STA detects the first symbol of the known sequence correctly after the sounding procedure (depicted here with the white star in Fig. 5), h±is fed back to AP1. Subsequently, AP1 can derive steering matrices with hl tand STA can receive signals with the channel gain h1w1. On the other hand, if the STA detects the first symbol of the known sequence incorrectly (depicted here with the black star), the STA will observes h2ej^ as channel between AP2 and STA, wherein A< > is defined as: p N, k, t) =where N is the FFT number, k is the subcarrier index (- < k < - 1) and Atsis the difference of detected samples. The STA will feed this back to AP2, and AP2 will subsequently derive steering matrices w2optimized for h2ejk^. Accordingly, if the STA detects the first symbol of the known sequence correctly, the STA observes received signals with channel gain ofh1w1+ / i2W2, but w2isn’t optimized for h2but A similar problem arises when AP2 detects the timing of the trigger frame incorrectly, because typically AP2 sends a PPDll in NCJT fixed seconds after AP2 receives the trigger from AP1. In this case, even if STA detects correct timings, AP2 sends a signal a bit later than it should.

[0043] Accordingly, timing detection doesn't always give the same result and can therefore cause unwanted phase shifts in the received signals. A phase shift may also occur if AP1 starts to transmit slightly earlier than STA2 or vice versa for various reasons (e.g. clock differences). The amount of phase shift depends on the subcarrier frequencies in the baseband and / or the time differences between the correct timing and the detected timing if the frequency clocks of each device are the same.

[0044] Assuming OFDM is used for signal transmission, the value of phase shift A< > can be expressed as p N, k, t) =where N is the FFT number, k is the subcarrier index (- < k < - 1) and Atsis the difference of detected samples (i.e. one sample difference between white star and black star, in Fig. 5).

[0045] In view of the above, phase misalignment can be identified as a fundamental problem in NCJT that may lead to signal cancellation. Specifically, two problems may arise from phase misalignment with respect to the NCJT in diversity mode: (i) signal cancellation due to individual steering matrix calculation at the APs, which cannot guarantee the same phase between the received signals, and (ii) signal cancellation due to transmitted signals not being received at the same time or due to timing detection errors at the STA, which do not capture the correct timing.

[0046] Both issues are commonly addressed and mitigated according to an aspect of this disclosure. According to various embodiments of the present disclosure alignment configuration information is exchanged between the APs to mitigate signal cancellation.

[0047] Fig. 6 shows a schematic diagram of an embodiment according to the present disclosure. In Fig. 6, a first communication device 601 (i.e., AP1) is configured to communicate with a thirdcommunication device 602 (i.e., STA) in cooperation with a second communication device 603 (i.e, AP2). The first communication device 601 and the second communication device 603 can be configured to provide at least partially same data to the third communication device 603 using JT, particularly NCJT.

[0048] In order to avoid signal cancellation due to the reasons described above, the first communication device 601 transmits alignment configuration information 604 to the second communication device 602, based on which the first and / or the second communication device 601 , 602 can change one or more configuration parameters to avoid signal cancellation of received signals. The alignment configuration information 604 includes at least one of subcarrier selection information and phase alignment information. The latter may include an expected complex gain information. As will be explained in more detail below, the phase alignment information can mitigate signal cancellation due to individual steering matrix calculation, and the subcarrier selection information can mitigate signal cancellation due to transmitted signals not being received at the same time or due to timing detection errors.

[0049] For instance, the subcarrier selection information can include one or more subcarriers and / or a range of subcarriers to be jointly used by the first communication device 601 and second communication device 602 for coordinated communication with the third communication device 603. The coordinated communication is this case may be NCJT in diversity mode. Specifically, each subcarrier to be jointly used can be selected such that a frequency distance between direct current, DC, frequency subcarrier and the each of the one or more subcarriers to be jointly used in the coordinated communication is less than a frequency distance between the DC frequency subcarrier and each of one or more subcarriers not used for the coordinated communication. In other words, preferably lower frequency subcarriers are being used for diversity-mode NCJT to mitigate phase misalignment to timing issues.

[0050] Alternatively or in addition to the subcarrier selection information, phase alignment (PA) information can be exchanged between APs as alignment configuration information. With the phase alignment Information, the first communication device 601 (e.g. AP1) can inform the second communication device 602 (e.g. AP2) about phase alignment of a received signal (i.e.h1w1, h2w2Subsequently, AP2 can derive steering matrices w2ejeto avoid signal cancelation and maximize+ h2w2eje| at best.

[0051] Fig. 7 is a frame exchange sequence illustrating the exchange of phase alignment information according to a first embodiment. In Fig. 7, a first communication device 701 (i.e., AP1) is configured to communicate with a third communication device 703 (i.e., STA) in cooperation with a second communication device 702 (i.e., AP2). The first communication device 701 and the second communication device 702 have same data to send to the third communication device 703. For simplicity, it is assumed that the data is already scrambled in the same way and that the same FEC (Forward Error Check) is used, such as LDPC (Low-Density Power Code) or BCC (Binary Convolutional Code). It is understood that the data may also be provided in the appropriate format from another device (i.e., a Master AP connected with both the first communication device 701 and the second communication device 702).

[0052] The frame sequence starts by initiating a joint sounding procedure so that NDPs can be detected at the same time by the third communication device 703. The first communication device 701 transmits a sounding trigger 704 to the second communication device 702, followed by an NDPA 705A to the third communication device 703 at a defined offset. In response to receiving the sounding trigger 704, the second communication device 702 transmits an NDPA 705B to the third communication 703, preferably simultaneously to the first communication device 701. The NDPA 705B of the second communication device 702 is optionally. Next, both the first communication device 701 and the second communication device 702 send an NDP 706A, 706B to the third communication device 703. To conclude the sounding procedure, the third communication device 703 transmits a CSI-FBCK 707 to the first communication device 701 and the second communication device 702. To allow the first communication device 701 and the third communication device 702 to be aware of a phase of expected received signals in NCJT, Non-Compressed FBCK or a channel matrix shall be informed to third communication device 703 as a format for the CSI-FBCK 707, and the third communication device 703 transmits the CSI-FBCK 707 to the first communication device 701 and the second communication device 702 in the requested format and with the requested content. The first communication device 701 receives at least CSI-FBCK for the channel between the first communication device 701 and the third communication device703, and the second communication device 702 receives at least CSI-FBCK for the channel between the second communication device and the third communication device 703.

[0053] After receiving the CSI-FBCK 707, both the first communication device 701 and the second communication device 702 derive steering matrices to the third communication device 703 from their respective CSI. Specifically, the first communication device 701 and / or the second communication device 702 calculate expected phase of the received signals at the third communication device 703 with the steering matrices, at least for one receive antenna.

[0054] After calculating the steering matrices, either the first communication device 701 or the second communication device 702 sends the counterpart expected magnitude and / or phase of the received signal at the third communication device 703 to the respective other communication device as the phase alignment information. In the example of Fig. 7, the first communication device 701 transmits phase alignment information to the second communication device 702. The PA frame is denoted here with reference numeral 708. Subsequently, the second communication device 702 derives the coefficient eJ'6'oPt, which is multiplied with w2, for its steering matrices to avoid signal cancelation of transmitted PPDll at the third communication device 703, and potentially to yield diversity gain as much as possible. In the following, two examples of calculating the coefficient ej6'oPtare illustrated. In a first case, magnitude and phase of hi lw1for all receive antenna are informed within the PA, and in a second case only phase of hi lw1is informed within the PA.

[0055] In case 1 : If the first communication device 701 sends to the second communication device 702 an indication of expected complex channel gain hi lw1for all receive antennas, the second communication device 702 can derive the phase coefficient 6optas follows:and under the assumption that the third communication devicesperforms Maximum Ratio Combining (MRC) when receiving a PPDll in the following NCJT.Furthermore, hi bis a estimated channel vector between the third communication devices’ j-th antenna and the b-th commuinctaion device, and wcis the c-th communication devices' steering matrix.

[0056] The first communication device 701 and the second communication device 702 may include within a NCJT trigger frame 709, which indicates start of JT, an indication that the coefficient is calculated under assumption that the second communication uses MRC in its MIMO (Multi- Input-Multi-Output) equalizer.

[0057] Fig. 8 shows a frame diagram illustrating an example of a PA frame 800 for case 1 . PA frame 800 can include the following subfields: (i) NCJT D-Mode REQ field 801 indicating that diversity-mode NCJT will be performed among one or more communication devices (e.g. AP1 and AP2). This field can be omitted if a NCJT trigger including this field is sent prior to the PA frame, (ii) BW field 802 indicating the bandwidth for the upcoming diversity-mode NCJT. This field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame containing the same information, (iii) NCJT D-Mode Rll field 803 indicating the resource unit(s) (Rll) via which the same data is carried to the destination in the upcoming diversitymode NCJT. This field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame contain the same information, (iv) Destination field 804 indicating the destination in the upcoming diversity-mode NCJT. The field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame containing the same information, (v) Expected Complex Gain field 805 indicating the phase or the complex value of hi lw1for all receive antennas.

[0058] In case 2: If the first communication device 701 (i.e. , AP1) sends to the second communication device 702 (i.e., AP2) an indication of a phase § of an expected received signal the second communication device 702 derives the phase coefficient 6optsuch that § = angle hii2W2ejeoPtThe first communication device 701 may send the phase § for each subcarrier to be used in NCJT at least for one receive antenna.

[0059] Fig. 9 shows a frame diagram illustrating an example of a PA frame 900 for case 2. The PA frame 900 can include the following subfields: (i) NCJT D-Mode REQ field 901 indicating that diversity-mode NCJT will be performed among one or more communication devices (e.g. AP1 and AP2). This field can be omitted if a NCJT trigger including this field is sent prior to the PA frame, (ii) BW field 902 indicating the bandwidth for the upcoming diversity-mode NCJT. This field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame containing the same information, (iii) NCJT D-Mode Rll field 903 indicating the resource unit(s) (Rll) via which the same data is carried to the destination in the upcoming diversitymode NCJT. This field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame contain the same information, (iv) Destination field 904 indicating the destination in the upcoming diversity-mode NCJT. The field can also be omitted if a NCJT trigger including this field is sent prior to the PA frame containing the same information, (v) Expected Phase field 905 indicating a phase of an expected received signal at the antenna indicated in a Rx Ant field 906 of the destination. This Expected Phase field 905 may indicate phases for all Rll indicated in NCJT D-Mode Rll field 903, or just one phase for one subcarrier in the Rll. (vi) Rx Ant field 906 indicating the destination’s receive antenna for which the phase is indicated by the Expected Phase field 905. (vii) Phase offset over Rll field 907 indicating expected phase of a received signal at the receive antenna indicated in the Rx Ant field 906 of the destination indicated in Destination field 904 on subcarriers in the Rlls indicated in the NCJT D-Mode Rll field 903. This field may only be included if in the Expected Phase field 905 only the phase for one subcarrier is indicated. To derive the phase, indication in the Expected Phase field 905 shall jointly be used. For example, if the Expected Phase field 905 indicates only 0O, the second communication device (i.e. , AP2) can assume that phase of an expected received signal from the first communication device (i.e., AP1) to the third communication device 703 (i.e., STA) is 0( / c) according to:0( / c) = k90where k is an arbitrary subcarrier index among the Rlls indicated in NCJT D-Mode Rll field 903.

[0060] Returning to the frame exchange sequence of Fig. 7. After the phase alignment information has been exchanged with any of the above information, the first communication device 701sends a NCJT trigger 709 to the second communication device 702 and, with a defined offset, a first PPDll 710A to the third communication device 703. The second communication device 702 receives the NCJT trigger 709 indicating start of NCJT and prepares a PPDll 710B containing substantially the same or partially the same data as the PPDll 710A. The second communication device 702 then transmits the PPDU 71 OB to the third communication device 703, preferably simultaneously with the first communication device 701. The third communication device 703 receives both PPDUs 710A, 710B and responds with an acknowledgement (ACK) 711 , which it transmits to the first communication device 701 and the second communication device 702.

[0061] As outlined above, subcarrier selection information can also be exchanged between the communication devices performing NCJT within the alignment configuration information. One can distinguish between a single user (SU) case and a multi user (MU) case.

[0062] In case 1 of subcarrier assignment: To avoid burst errors, quadrature amplitude modulation (QAM) symbols are typically assigned to subcarriers such that adjacent QAM symbols are not assigned to adjacent subcarriers. This subcarrier allocation is called interleaving and / or tone mapping, which are essentially the same thing. As mentioned above, phase shift can still occur if the start times of the signals are slightly different among the communication devices performing JT due to various reasons, and a subcarrier allocation design is needed to mitigate the resulting phase shift. One of the subcarrier allocation designs is that the first communication device (i.e., AP1) and the second communication device (i.e., AP2) allocate the same QAM symbols to the same subcarriers where the phase shift doesn't affect the performance so much, i.e. the phase shift is less severe in diversity mode NCJT. For instance, the subcarriers could be subcarriers close to the DC component. For other communication than NCJT in diversity mode, the first communication device (i.e., AP1) and the second communication device each allocate QAM symbols to different subcarriers than the ones selected for NCJT.

[0063] For example, assuming QAM symbols are allocated to one subcarrier among the — / V-th to + / V-th subcarriers, then subcarriers from - Z-th to + Z-th ( / < N) are less affected by phase shift in diversity-mode NCJT, while other subcarriers from- / V -th to -( / + l)-th and from(Z + l)-th to 7V-th, are more affected by phase shift. Consequently, for subcarrier mapping, the first and second communication device (i.e. , AP1 and AP2) allocate first QAM symbols to subcarriers from - Z-th to Z-th for NCJT. Furthermore, the first communication device (i.e, AP1) may allocate second QAM symbols to subcarriers from (Z + l)-th to AZ-th, while the second communication device (i.e, AP1) allocates second QAM symbols to subcarriers from — (Z + l)-th to —AZ-th.

[0064] Fig. 10 shows an exemplary subcarrier mapping of the first communication device and the second communication device (i.e., AP1 and AP2). Both devices allocate same data symbols 1001A, 1001 B on lower frequency subcarriers (i.e., subcarrier with index close to 0 (-1-1 in Fig. 10). For other symbols not to be send jointly, the first and second communication device use other subcarriers not used for the NCJT. For example, the first communication device (i.e., AP1) performs subcarrier mapping according to the following mapping function: r( , -Z, AZ)Then, the second communication device (i.e., AP2) can perform subcarrier mapping according to the following mapping function:Accordingly, both the first communication device and the second communication device (i.e., AP1 and AP2) send the same QAM symbols on subcarrier indices from -Z to +Z, but subcarrier indices from (Z + 1) to AZ are used by the first communication device, while subcarrier indices from -AZ to - (Z + 1) are used by the second communication device. This allows receivers to obtain channel diversity gain by jointly received signals on subcarrier indices -Z and +Z while avoiding signal cancelation.

[0065] In case 2, MU communication is performed while simultaneously SU communication is provided for NCJT. Accordingly, the first and second communication device (i.e., AP1 and AP2) may send different data to different communication devices while sending common data jointly in diversity-mode NCJT to a common communication device (i.e., the third communication device). In this case, subcarriers for NCJT to the common communicationdevice can be allocated from subcarrier index -I to I, using subcarrier mapping function f (i, -I, +Z) at both the first and second communication device. The other subcarriers can be allocated for data transmission to the different communication devices. For example, subcarrier indices ( / + 1) to N carry data from the first communication device (i.e. , AP1) to one of the other different communication devices, and the subcarrier indices —N to -( / + 1) carry data from the second communication device (i.e., AP2) to one of the other communication devices.

[0066] In order to signal the subcarrier selection to other communication devices signaling information in the preamble of a PPDll may be enhanced. For instance, to inform the different communication devices of the above parameter I and all subcarrier indices that are used to send data to the common communication device (NCJT mode), both of the first communication device and the second communication devices (i.e., AP1 and AP2) can indicate the value of I and the subcarrier indices in the preamble of a transmitted PPDll as user specific information.

[0067] Fig. 11 shows as frame diagram illustrating an example of extra signaling for NCJT in the preamble 1100 of a PPDll. In the preamble 1100 three additional fields may be transmitted in a SIG field 1101. There fields include: (i) NCJT Mode field 1102, (ii) BW field 1103 and (iii) NCJT D-Mode RU field 1104. The NCJT Mode field 1102 is an indication that the transmitted PPDU contains data to be sent according to diversity-mode NCJT. The BW field 1103 is an indication as to which group of subcarriers carry data for the communication device that is jointly served. The NCJT D-Mode RU field 1103 is an indication which subcarriers among those indicated in BW field 1103 carry data for diversity-mode NCJT.

[0068] Returning to the frame exchange sequence shown in Figure 7. The second communication device 703 and other communication devices (not depicted here) receive PPDUs from both the first communication device 701 and the second communication device 702 (i.e., AP1 and AP2). An example of a preamble of these PPDUs is outlined in Fig. 11. From the preamble recipients can extract which RUs carry the same data for diversity-mode NCJT and which RUs carry different data.

[0069] Moreover, the third communication device 703 can additionally improve SNR by using the recommended MIMO equalizer algorithm (e.g. MRC) after equalization, if the NCJT Trigger or PPDll indicates it. Clipping noise may also be an issue if the first communication device 701 and the second communication device 702 start transmitting signals at slightly different times. Auto Gain Control (AGC) activates upon receiving the first signal from either the first communication device 701 or the second communication device 702. However, if a second signal from another APs is received after AGC is set, the combined signal may exceed the largest signal that the third communication device 703 can observe without clipping noise. To prevent this issue, the third communication device 703 may allow for some power headroom (e.g. 3dB) when receiving a signal.

[0070] Fig. 12 is a frame exchange sequence illustrating the exchange of phase alignment information according to a second embodiment. In Fig. 12, a first communication device 1201 (i.e. , AP1) communicates with a third communication device 1203 (i.e, STA) in cooperation with a second communication device 1202 (i.e, AP2). The first communication device 1201 and the second communication device 1202 have same data to send to the third communication device 1203. For simplicity, it is assumed that the data is already scrambled in the same way and that the same FEC (Forward Error Check) is used, such as LDPC (Low- Density Power Code) or BCC (Binary Convolutional Code). It is understood that the data may also be provided in the appropriate format from another device (i.e., a Master AP, connected with both the first communication device 1201 and the second communication device 1202).

[0071] The second embodiment of FIG. 12 differs from the first embodiment of FIG. 7 in that in the second embodiment, the third communication device (i.e., the STA to be jointly served) provides the phase alignment information to the first communication device and the second communication device performing NCJT. In other words, a STA informs of a target phase for upcoming diversity-mode NCJT instead of an AP as in the first embodiment . Accordingly, the phase alignment information does not need to be exchanged between the first communication device 1201 and second communication device 1202 that perform NCJT in diversity mode.

[0072] Similar, to the first embodiment of Fig. 7, a joint sounding procedure is performed before NCJT is started. The first communication device 1201 sends a sounding trigger 1204 to the second communication device 1202 and, with a defined offset, an NDPA 1205A to the third communication device 1203. In response to the sounding trigger 1204, the second communication device 1202 transmits an NDPA 1205B to the third communication device 1203, as in the first embodiment of Fig. 7. Furthermore, as in the first embodiment of Fig. 7, the NDPA is followed by NDPs 1206A, 1206B from the first communication device 1201 and the second communication device 1202 to the third communication device 1203. The NDPAs of the first communication device 1201 and second communication device 1202 are preferably send simultaneously. Likewise, the NDPs of the first communication device 1201 and second communication device 1202 are preferably send simultaneously.

[0073] Different to the first embodiment of Fig. 7, the NDPAs according to the second embodiment include an indication that the joint sounding is for a NCJT which is to follow. Based on the additional information the second communication device 1202 is aware that data will be send jointly from the first communication device 1201 and the second communication device 1202. Accordingly, the third communication device 1203 calculates CSI for both the first communication device 1201 and the second communication device 1202 and sends CSI- FBCK in the form of Non-Compressed Feedback to both devices including additional fields as phase alignment information. The CSI-FBCK frame including the additional fields is denoted here with reference numeral 1207.

[0074] Fig. 13 is a frame diagram illustrating the additional fields included in a CSI-FBCK frame. The fields include (i) a NCJT D-Mode Target Phase field 1301 , (i) a Rx Ant field 1302, and (iii) a Phase offset over Rll field 1304. The NCJT D-Mode Target Phase field 1301 indicates the target phase of a received signal at an antenna specified in the Rx Ant field 1302 of the third communication device 1203 in the upcoming diversity-mode NCJT. The Rx Ant field 1302 indicates the third communication device’s received antenna, for which the phase is indicated tin the NCJT D-Mode Target Phase field 1301. The Phase offset over Rll field 1304 indicates the target phase of received signal at the receive antenna indicated in the Rx Ant field 1302 of the third communication device 1203 in the upcoming diversity-mode NCJT.

[0075] Based on the additional fields, the first communication device 1201 and the second communication device 1202 can set the target phase e( / c) of the received signal in the upcoming diversity-mode NCJT as expressed in: 0( / c) = k90where k is an arbitrary subcarrier index among Rlls in which NDPs are sent and 90is indicated in the NCJT D-Mode Target Phase field 1301.

[0076] Fig. 14 shows a flow chart of an embodiment of a first communication method 1400 of a first communication device (e.g. AP1) configured to communicate with a third communication device (e.g. STA) in coordination with a second communication device (e.g. AP2). In a first step 1401 , the first communication device receives channel feedback information from the third communication device in response to a sounding procedure. In a second step 1402, the first communication device determines alignment configuration information based on the channel feedback information. The alignment configuration information includes at least one of subcarrier selection information and phase alignment information according to any one of the examples as outlined above. In a third step 1403, the first communication device transmits the alignment configuration information to the second communication device. Subsequently, in a fourth step 1404, the first communication device communicates with the third communication device in coordination with the second communication device by transmitting to the third communication device an indicator indicating use of coordinated communication.

[0077] Fig. 15 shows a flow chart of an embodiment of a second communication method 1500 of a second communication device (e.g. AP2) configured to communicate with a third communication device (e.g. STA) in coordination with a first communication device (e.g. AP1). In a first step 1501 , the second communication device receives channel feedback information from the third communication device in response to a sounding procedure. Next, in a second step 1502, the second communication device receives, from the first communication device or the third communication device, alignment configuration information. The alignment configuration information includes at least one of subcarrier selection information and phase alignment information according to any one of the examplesas outlined above. Finally, in a third step 1503, the second communication device communicates with the third communication device in coordination with the first communication device based on the received alignment configuration information.

[0078] Fig. 16 shows a flow chart of an embodiment of a third communication method 1600 of a third communication device (e.g. STA) configured to receive data in a coordinated communication from a first communication device (e.g. AP1) in coordination with a second communication device (e.g. AP2). In a first step 1601 , the third communication device receives a sounding information from the first and / or second communication device. In a second step 1602, the third communication device determines alignment configuration information based on the sounding information. The alignment configuration information includes at least one of subcarrier selection information and phase alignment information according to any one of the examples as outlined above. Next, in a third step 1603, the third communication device transmits, in response to a request by the first and / or the second communication device, the alignment configuration information to the first communication device and the second communication device. Finally, in a fourth step 1604, the third communication device receives from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.

[0079] In summary, the present disclosure presents communications devices and method that facilitate use of joint transmission, in particular for diversity-mode NCJT. Specifically, embodiments of the present disclosure can avoid signal cancelation due to phase misalignment. In various embodiments, the phase misalignment is addressed by phase alignment of the received signalh2w2), and not by phase alignment of a steering matrix. Furthermore, in various embodiments phase misalignment caused by reception timing differences is addressed by allocating data for NCJT to lower frequency subcarriers.

[0080] The device may be implemented by respective units or circuitry, e.g. a processor, processing circuitry, a computer, dedicated hardware, etc., that carries out the functions of the device. Alternatively, a common unit or circuitry, e.g. a common processor or computer, mayimplement the various functions of the device, or separate units or elements may be used that together represent the circuitry.

[0081] Thus, the foregoing discussion discloses and describes merely exemplary embodiments of the present disclosure. As will be understood by those skilled in the art, the present disclosure may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. Accordingly, the disclosure of the present disclosure is intended to be illustrative, but not limiting of the scope of the disclosure, as well as other claims. The disclosure, including any readily discernible variants of the teachings herein, defines, in part, the scope of the foregoing claim terminology such that no inventive subject matter is dedicated to the public.

[0082] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0083] In so far as embodiments of the disclosure have been described as being implemented, at least in part, by software-controlled data processing apparatus, it will be appreciated that a non-transitory machine-readable medium carrying such software, such as an optical disk, a magnetic disk, semiconductor memory or the like, is also considered to represent an embodiment of the present disclosure. Further, such a software may also be distributed in other forms, such as via the Internet or other wired or telecommunication systems.

[0084] The elements of the disclosed devices, apparatus and systems may be implemented by corresponding hardware and / or software elements, for instance appropriate circuits or circuitry. A circuit is a structural assemblage of electronic components including conventional circuit elements, integrated circuits including application specific integrated circuits, standard integrated circuits, application specific standard products, and field programmable gate arrays. Further, a circuit includes central processing units, graphics processing units, and microprocessors which are programmed or configured according to software code. A circuitdoes not include pure software, although a circuit includes the above-described hardware executing software. A circuit or circuitry may be implemented by a single device or unit or multiple devices or units, or chipset(s), or processor(s).

[0085] It follows a list of further embodiments of the disclosed subject matter:1. First communication device configured to communicate with a third communication device in coordination with a second communication device, the first communication device comprising circuitry configured to: transmit a sounding information to the third communication device, receive channel feedback information from the third communication device in response to the sounding information, determine alignment configuration information based on the channel feedback information and transmit the alignment configuration information to the second communication device, or receive alignment configuration information from the third communication device and determined by the third communication device based on the sounding information, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the second communication device.2. First communication device according to embodiment 1 , wherein the circuitry is configured to transmit at least partially the same data to the third communication device as is transmitted by the second communication device when communicating with the third communication device in coordination with the second communication device.3. First communication device according to embodiment 2, wherein the circuitry is configured to transmit the at least partially same data in coordination with the second communication device by a non-coherent joint transmission, NCJT, in a diversity mode.4. First communication device according to any one of embodiments 1 to 3, wherein the indicator includes at least one of (i) an indication that a physical protocol data unit, PPDll,transmitted from the first communication device is sent in joint transmission with the second communication and (ii) an indication of at least one subcarrier used for joint transmission from the first communication device and the second communication device.5. First communication device according to any one of embodiments 1 to 4, wherein the subcarrier selection information includes one or more subcarriers and / or a range of subcarriers to be jointly used by the first communication device and second communication device for the coordinated communication with the third communication device.6. First communication device according to embodiment 5, wherein a subcarrier not indicated in the subcarrier selection information is not used for coordinated communication with the third communication device.7. First communication device according to embodiment 5 or 6, wherein a frequency distance between direct current, DC, frequency subcarriers and the one or more subcarriers to be jointly used is less than a frequency distance between the DC frequency subcarriers and the one or more subcarriers not jointly used.8. First communication device according to any one of embodiments 1 to 7, wherein the circuitry is further configured to: derive a steering matrix from the channel feedback information, generate expected phase information of a received signal at the third communication device based on the channel feedback information and the steering matrix, and transmit the generated expect phase information as the phase alignment information to the second communication device.9. First communication device according to embodiment 8, wherein the expect phase information includes a complex channel gain information for all receive antennas of the third communication device.10. First communication device according to embodiment 9, wherein the circuitry is further configured to:calculate, for at least one receive antenna of the third communication device, an expected phase of the received signal at the at least one receive antenna of the third communication device based on the channel feedback information, and transmit the calculated expect phase and an indicator indicating the at least one receive antenna as the phase allocation information to the third communication device.11. First communication device according to any one of embodiments 1 to 10, wherein the circuitry is further configured to transmit a trigger to the second communication device indicating start of coordinated communication, the second communication device starting the coordinated communication in response to the trigger.12. First communication device according to any one of embodiments 1 to 11 , wherein the circuitry is further configured to transmit a sounding trigger to the second communication device indicating start of a coordinated sounding procedure, the second communication device starting the coordinated sounding procedure in response to the sounding trigger.13. First communication device according to any one of embodiments 1 to 12, wherein the circuitry is further configured to transmit a physical protocol data unit, PPDll, having a preamble to the third communication device, the preamble including the indicator indicating use of coordinated communication.14. First communication device according to embodiment 12, wherein the preamble further includes the subcarrier selection information.15. First communication device according to any one of embodiments 1 to 14, wherein the circuitry is further configured to communicate with the third communication device in coordination with the second communication device by transmitting to the third communication device an indicator indicating use of coordinated communication.16. First communication device according to any one of embodiments 1 to 15, wherein the circuitry is further configured to transmit a request to the third communication device requesting the third communication device to transmit the alignment configuration information.17. Second communication device configured to communicate with a third communication device in coordination with a first communication device, the second communication device comprising circuitry configured to: receive a sounding information for the third communication device, receive channel feedback information from the third communication device in response to the sounding information, receive, from the first communication device or the third communication device, alignment configuration information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the first communication device based on the received alignment configuration information.18. Second communication device according to embodiment 17, where in the circuitry is configured to derive a steering matrix from the channel feedback information and the alignment configuration information.19. Second communication device according to embodiment 17 or 18, wherein the circuitry is configured to transmit at least partially the same data to the third communication device as is transmitted by the first communication device when communicating with the third communication device in coordination with the first communication device.20. Second communication device according to any one of embodiments 17 to 19, wherein the circuitry is configured to: receive a trigger from the first communication device indicating a start of coordinated communication, and start communicating with the third communication device in coordination with the first communication device in response to the trigger.21. Second communication device according to any one of embodiments 17 to 20, wherein the circuitry is further configured to: receive a sounding trigger from the first communication device indicating a start of a coordinated sounding procedure, andtransmit a training signal to the third communication device in response to receiving the sounding trigger.22. Second communication device according to any one of embodiments 17 to 21 , wherein the circuitry is further configured to communicate with the third communication device in coordination with the first communication device by transmitting to the third communication device an indicator indicating use of coordinated communication.23. Second communication device according to any one of embodiments 17 to 22, wherein the circuitry is further configured to transmit a request to the third communication device requesting the third communication device to transmit the alignment configuration information.24. Third communication device configured to receive data in a coordinated communication from a first communication device in coordination with a second communication device, the third communication device comprising circuitry configured to: receive a sounding information from at least one of the first communication device and the second communication device, determine alignment configuration information based on the sounding information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, transmit, in response to a request by at least one of the first communication device and the second communication device, the alignment configuration information to the first communication device and the second communication device, and receive from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.25. Third communication device according to embodiment 24, wherein the circuitry is further configured to receive an indicator from the first communication device and / or the second communication device, the indicator indicating use of the coordinated communication.26. First communication method of a first communication device configured to communicate with a third communication device in coordination with a second communication device, the first communication method comprising: transmitting a sounding information to the third communication device, receiving channel feedback information from the third communication device in response to the sounding information, determining alignment configuration information based on the channel feedback information and transmitting the alignment configuration information to the second communication device, or receiving alignment configuration information from the third communication device and determined by the third communication device based on the sounding information, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicating with the third communication device in coordination with the second communication device.27. Second communication method of a second communication device configured to communicate with a third communication device in coordination with a first communication device, the second communication method comprising: receiving a sounding information for the third communication device, receiving channel feedback information from the third communication device in response to the sounding information, receiving, from the first communication device or the third communication device, alignment configuration information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, and communicating with the third communication device in coordination with the first communication device based on the received alignment configuration information.28. Third communication method of a third communication device configured to receive data in a coordinated communication from a first communication device in coordination with a second communication device, the third communication method comprising: receiving a sounding information from the first and / or second communication device,determining alignment configuration information based on the sounding information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, transmitting, in response to a request by at least one of the first communication device and the second communication device, the alignment configuration information to the first communication device and the second communication device, and receiving from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.29. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to any one of embodiments 26 to 28 to be performed.

Claims

CLAIMS1. First communication device configured to communicate with a third communication device in coordination with a second communication device, the first communication device comprising circuitry configured to: transmit a sounding information to the third communication device, receive channel feedback information from the third communication device in response to the sounding information, determine alignment configuration information based on the channel feedback information and transmit the alignment configuration information to the second communication device, or receive the alignment configuration information from the third communication device and determined by the third communication device based on the sounding information, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the second communication device.

2. First communication device according to claim 1 , wherein the circuitry is configured to transmit at least partially the same data to the third communication device as is transmitted by the second communication device when communicating with the third communication device in coordination with the second communication device.

3. First communication device according to claim 2, wherein the circuitry is configured to transmit the at least partially same data in coordination with the second communication device by a non-coherent joint transmission, NCJT, in a diversity mode.

4. First communication device according to claim 1 , wherein the indicator includes at least one of (i) an indication that a physical protocol data unit, PPDll, transmitted from the first communication device is sent in joint transmission with the second communication device and (ii) an indication of at least one subcarrier used for joint transmission from the first communication device and the second communication device.

5. First communication device according to claim 1 , wherein the subcarrier selection information includes one or more subcarriers and / or a range of subcarriers to be jointly used by the first communication device and second communication device for the coordinated communication with the third communication device.

6. First communication device according to claim 5, wherein a subcarrier not indicated in the subcarrier selection information is not used for coordinated communication with the third communication device.

7. First communication device according to claim 5, wherein a frequency distance between direct current, DC, frequency subcarriers and the one or more subcarriers to be jointly used is less than a frequency distance between the DC frequency subcarriers and the one or more subcarriers not jointly used.

8. First communication device according to claim 1 , wherein the circuitry is further configured to: derive a steering matrix from the channel feedback information, generate expected phase information of a received signal at the third communication device based on the channel feedback information and the steering matrix, and transmit the generated expect phase information as the phase alignment information to the second communication device.

9. First communication device according to claim 8, wherein the expect phase information includes a complex-valued channel gain information for all receive antennas of the third communication device.

10. First communication device according to claim 9, wherein the circuitry is further configured to: calculate, for at least one receive antenna of the third communication device, an expected phase of the received signal at the at least one receive antenna of the third communication device based on the channel feedback information, and transmit the calculated expect phase and an indicator indicating the at least one receive antenna as the phase allocation information to the third communication device.

11. First communication device according to claim 1 , wherein the circuitry is further configured to transmit a trigger to the second communication device indicating start of coordinated communication, the second communication device starting the coordinated communication in response to the trigger.

12. First communication device according to claim 1 , wherein the circuitry is further configured to transmit to the third communication device a physical protocol data unit, PPDll, having a preamble, the preamble including the indicator indicating use of coordinated communication.

13. Second communication device configured to communicate with a third communication device in coordination with a first communication device, the second communication device comprising circuitry configured to: receive a sounding information for the third communication device, receive channel feedback information from the third communication device in response to the sounding information, receive, from the first communication device or the third communication device, alignment configuration information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, and communicate with the third communication device in coordination with the first communication device based on the received alignment configuration information.

14. Second communication device according to claim 13, where in the circuitry is configured to derive a steering matrix from the channel feedback information and the alignment configuration information.

15. Second communication device according to claim 13, wherein the circuitry is configured to transmit at least partially the same data to the third communication device as is transmitted by the first communication device when communicating with the third communication device in coordination with the first communication device.

16. Third communication device configured to receive data in a coordinated communication from a first communication device in coordination with a second communication device, the third communication device comprising circuitry configured to: receive a sounding information from at least one of the first communication device and the second communication device, transmit channel feedback information to the first or second communication device.” determine alignment configuration information based on the sounding information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, transmit, in response to a request by at least one of the first communication device and the second communication device, the alignment configuration information to the first communication device and the second communication device, and receive from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.

17. First communication method of a first communication device configured to communicate with a third communication device in coordination with a second communication device, the first communication method comprising: transmitting a sounding information to the third communication device, receiving channel feedback information from the third communication device in response to a sounding information, determining alignment configuration information based on the channel feedback information and transmitting the alignment configuration information to the second communication device, or receiving alignment configuration information from the third communication device and determined by the third communication device based on the sounding information, wherein the alignment configuration information includes at least one of subcarrier selection information and phase alignment information, and communicating with the third communication device in coordination with the second communication device.

18. Second communication method of a second communication device configured to communicate with a third communication device in coordination with a first communication device, the second communication method comprising: receiving a sounding information for the third communication device, receiving channel feedback information from the third communication device in response to the sounding information, receiving, from the first communication device or the third communication device, alignment configuration information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, and communicating with the third communication device in coordination with the first communication device based on the received alignment configuration information.

19. Third communication method of a third communication device configured to receive data in a coordinated communication from a first communication device in coordination with a second communication device, the third communication method comprising: receiving a sounding information from at least one of the first communication device and the second communication device, determining alignment configuration information based on the sounding information, the alignment configuration information including at least one of subcarrier selection information and phase alignment information, transmitting, in response to a request by at least one of the first communication device and the second communication device, the alignment configuration information to the first communication device and the second communication device, and receiving from the first communication device a first frame and from the second communication device a second frame, the first frame and the second frame being transmitted based on the alignment configuration information and comprising at least partially same data.

20. A non-transitory computer-readable recording medium that stores therein a computer program product, which, when executed by a processor, causes the method according to any one of claims 17 to 19 to be performed.

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